This invention relates to multi-stage gas compressors for providing compressed gas at high flow rates and high pressures.
Many varied construction and maintenance activities benefit from the use of portable engine-driven gas compressors. For example, in servicing oil and gas wells, compressed air at high flow rates and high pressures is used to blow collected debris that is interfering with the flow of oil or gas from the well, and compressed air at substantially lower pressures, is used in maintaining structures exposed to the elements, for example, in sand blast cleaning and painting of steel bridges. Because such activities take place in remote locations, gas compressors are frequently engine-driven and carried by trailers or truck beds to the site of their use. Since the engine-driven gas compressors are operated in locations remote from sources of gasoline and diesel fuel, it is important that they provide maximal supplies of compressed gas with minimal fuel usage. It is important that such portable gas compressors be as efficient and reliable as possible, that they be as small and light as possible, and that their initial and operating costs be as low,as possible.
A number of compressed gas generators adapted for such remote use have been disclosed.
U.S. Pat. No. 4,496,291 discloses a compound turbocharger system for supplying air under pressure to an engine/compressor unit of the type illustrated in U.S. Pat. No. 4,232,997. The disclosed engine/compressor unit comprises a converted V-8 compression ignition engine, such as that manufactured by the Cummins Engine Company, Inc. of Columbus, Ind., and identified by their designation V-903.In such converted engine/compressor units, one bank of cylinders is left in its normal condition for operation as an internal combustion engine while the opposite bank of cylinders is modified so each modified cylinder can operate as an air compressor cylinder. More particularly, a new head for the compressor bank and valve operating arrangement is provided. Each cylinder in the compressor bank is isolated from the engine fuel supply, and valves are provided to cause air to be supplied to each compression cylinder during the corresponding piston downstroke and to cause compressed air to be exhausted from each cylinder during the corresponding piston upstroke. The air discharged from the compressor bank of cylinders is collected by an outlet manifold and may be supplied to a storage tank or to an apparatus utilizing or driven by compressed air.
In the compound turbocharger system disclosed by U.S. Pat. No. 4,496,291, two or more turbochargers driven by the exhaust gas from the bank of cylinders operating as an internal combustion engine compress atmospheric air and deliver the flow of compressed air to both the bank of cylinders operating as an internal combustion engine and the bank of cylinders operating as an air compressor.
By applying two specifically configured turbochargers in series to an engine-driven compressor such as that disclosed in U.S. Pat. No. 4,496,291, the output of the compressor can be increased by 33%; however, gains in performance of such systems are limited by the pressures and temperatures imposed on the engine exhaust system and only slight improvements can be further realized using current technology with the system of U.S. Pat. No. 4,496,291.
Another multi-stage compressor system with a monoblock construction is disclosed in U.S. Pat. No. 5,400,751, issued Mar. 28, 1995 to John Grimmer et al.
Other prior art systems include, for example, converted V-8 engine blocks which are modified so that all eight cylinders act as air compression cylinders, with all of the cylinders of one bank of cylinders operating in parallel to provide one stage of compression and with the cylinders of the second bank of cylinders operating in series to provide additional stages of compression that compress gas received from the first bank of cylinders. Thus, when the crankshaft of such a converted V-8 engine block is driven by an external power source, air supplied to the first bank of cylinders is compressed by their pistons and delivered to the second bank of cylinders for further stages of compression by the pistons and cylinders of the second bank of cylinders. In converting such engine blocks to a multi-stage compressor, the cylinders provide progressively smaller diameters and volumes so they may further compress the compressed gas received from the upstream compression cylinders. The sizing of the reciprocating pistons to keep operating temperatures within acceptable limits is known in the compressor art. One such system is sold by Hurricane Compressors of Franklin, Ind., as Production Model 903-84, which develops 330 cu. ft. per minute of compressed air taken from standard atmospheric pressure to 2000 psi and requires about 68 hp per 100 cu. ft. of compressed gas output.
Improved multi-stage gas compression systems which may be adapted to portable use with decreased size, improved reliability, improved efficiency and lower initial and operating costs are needed by industry.